RFR: 7903459: Update changelog for jtreg 7.2

[Christian Stein]

Please review this commit that updates the changelog file to include a section for jtreg 7.2.

It also adds the entry to the list of noteworthy unreleased changes of the upcoming jtreg 7.3 release.

-------------

Commit messages:
 - 7903459: Update changelog for jtreg 7.2

Changes: https://git.openjdk.org/jtreg/pull/150/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=150&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903459
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtreg/pull/150.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/150/head:pull/150

PR: https://git.openjdk.org/jtreg/pull/150